1. Field of the Invention
The present invention relates to a semi-conductor laser device adapted for use as a light source for example for an electrophotographic recording apparatus, and more particularly to a compact semi-conductor laser device capable of providing a parallel beam by collimation of the emergent beam from a laser chip by means of an incorporated lens.
2. Description of the Prior Art
Though a semi-conductor laser chip generally emits a diverging light beam with a divergent angle of 10.degree. to 40.degree., it is desirable to obtain a parallel beam from the semi-conductor laser device since the working efficiency becomes very low unless the beam is collimated with a lens in the vicinity of the light-emitting point, and also since a parallel beam is most convenient for optical handling.
The device already known for this purpose is composed, as shown in FIG. 1, of a lens unit 2 for collimating the diverging beam and an independent light-emitting unit 3, which are mechanically combined by connecting members 4 and 5. The lens unit 2 is composed of plural spherical lenses 2a, 2b, 2c for satisfying the required optical performance, with strict dimensional precision for each lens and for mutual relationship of the lenses.
The light-emitting unit 3 is provided with a casing 8 for protecting a laser chip 6 in a dry nigrogen atmosphere 7, in order to prevent the deterioration of said chip by oxidation caused by operation in ordinary atmosphere, said casing being equipped with a light-emitting glass port 9.
In the combination of these two units, a precise positioning is required with respect to the aberration between the optical axes and in focusing of the lens unit 2 and the laser chip 6.
If the optical axes are mutually aberrated, the beam emerging from the semi-conductor laser device becomes angularly aberrated from the optical axis of the lens unit 2, thus resulting in a beam displacement from the required position if the beam is utilized at a distant point from the light-emitting point. The tolerance for aberration of the optical axis, being determined as a function of the tolerance for said displacement, is generally in the range of 10.mu..
Also if the focusing is aberrated, the beam emerging from the semi-conductor laser device is not strictly parallel. Thus, in case said beam is to be focused to a spot, such non-parallel beam provides a focal point displaced from the desired position, resulting in a blurred spot at said desired position. The tolerance for aberration in focusing, being determined as a function of the tolerance for said blur, is generally in the range of 5.mu..
For the purpose of effectively collecting the light from a semi-conductor light-emitting element, Japanese Utility Model Laid-Open No. 9501/1980 discloses the use of an exit port having a light-converging lens function on the semi-conductor light-emitting element. However said invention is directed not to collimate the beam emerging from said element but to guide said beam effectively to a fiber bundle positioned in the vicinity of said exit port. Consequently the precision of mounting of said lens function element positioned close to the semi-conductor light-emitting element is far less critical than in the case of beam collimation.